Accurate, reliable, and robust numerical predictions
of the power required to turn the main rotor
blades of a rotorcraft remain a challenge to the
industry. Although various numerical methods do
exist and have been used in the design of many
different aircraft, there still remain some questions
regarding the prediction of the maximum power
required. Many of the existing theories do not work
well in this flight regime. One possible flaw is our
lack of understanding of how a rotor blade stalls
along the inboard radial locations.
To address this lack of understanding, NASA has
formed a collaborative effort with the Department of
Energy's (DoE) National Renewable Energy Laboratory
(NREL) to investigate the unsteady aerodynamics
of a horizontal axis wind turbine (HAWT). The main
purpose of this project is to gain a better understanding
of a wind turbine's unsteady aerodynamics. By
improving our understanding of this machine's
aerodynamic environment, we simultaneously
improve our capability to properly model rotorcraft
rotor blades.
In this effort, researchers use advanced rotorcraft
computational fluid dynamics (CFD) methods to
simulate the wind turbine. Solutions based on the
Reynolds-averaged Navier-Stokes equations have
been obtained as illustrated in figure 1. Concurrently,
NREL has installed and will test their Unsteady
Aerodynamics Experiment in NASA's 80- by 120-
Foot Wind Tunnel. This test is the largest and most
comprehensive wind tunnel test of an HAWT in the
world. It will provide extensive unsteady data
regarding, for example, pressure, air loads, and
dynamic blade response. The information gathered
from the experimental data, combined with the
knowledge obtained through the computations, forms
the nucleus for the development of more accurate
semi-empirical rotor design methods. In addition, the
knowledge gained through this collaborative program
will have a major effect on the understanding of other
rotary flow fields such as those of tilt rotors and
helicopters.
This collaborative effort directly addresses
aerodynamic issues relevant to both rotorcraft and
wind turbines. By utilizing scientific resources from
both NREL and NASA, we have been able to advance
our understanding of the aerodynamic behavior of
rotor blades to the benefit of both industries.
Point of Contact: E. Duque
(650) 604-4489
eduque@mail.arc.nasa.gov
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